On air with no voltage mods, it seems that the maximum clock speeds that can be achived are right in the neighborhood of 766MHz on the GPU cores and 1105MHz on the GDDR3 memory. I say this after benchmarking two reference design cards from different manufacturers that basically overclocked identically. The difference between the two cards clock speeds can be counted on one hand. The 166MHz overclock on the GPU core offers an increase in performance in many of the game benchmarks tested.

Keeping the cores cool by manually increasing the fan speed to 100 percent does help in achieving a higher overclock, just not more that 766MHz on the core in this case. 166MHz on the core and 105MHz on the memory are respectable overclocks when it comes down to it. When the CPU speed is ramped up the 9800GX2 takes off. This card from Palit performed almost identically the the XFX model I looked at several months ago. Scores of close to 19000 in 3DMark06 with the CPU at 3.6GHz show the potential of the card. While you can always hope for more ultimately what you get on air is what you get.

Read whole review: Palit 9800GX2